The present invention relates to mobile communication systems; and, more particularly, to methods of scheduling a time shared downlink packet data channel.
The demand for wireless data services, such as mobile Internet, video streaming, and voice over IP (VoIP), have led to the development of high speed packet data channels to provide high data rates needed for such services. High speed packet data channels are employed on the forward link in IS-2000 (also known as 1xEV-DV), IS-856 (also known as 1xEV-DO), and Wideband Code Division Multiple Access (WCDMA) systems. The high speed packet data channel is a time shared channel. Downlink transmissions, e.g., from a base station to the mobile stations, are time-multiplexed and transmitted at full power.
At any given time, the base station may transmit a packet to one or more mobile stations on the physical layer channel known as the downlink high speed packet data channel. Deciding which mobile station(s) to serve with the packet at a given time is the function of a “scheduler.” A number of different scheduling strategies can be used, each with a different implication for system throughput and fairness. Typical scheduling strategies employed include round-robin, maximum throughput, and proportional fairness. In addition, quality of service requirements frequently add scheduling complexities. For example, VoIP packet data, due to its conversational characteristic, typically has a relatively short maximum allowed transmission delay before service is considered to have unacceptably degraded. Thus, it is commonly necessary to schedule VoIP packet data for transmission more frequently than other packet data in order to maintain acceptable service.
However, simply scheduling VoIP packet data more frequently, without more, may result in inefficient use of available resources. This is because VoIP data is typically supplied at relatively low rate. As a result, VoIP data queued for transmission to a particular mobile station is typically less than a full packet's worth of data. Thus, if only that VoIP packet data is transmitted in a given physical layer packet, the packet is likely less than full, and typically significantly less than full. Transmitting less than full packets, particularly relatively lightly loaded packets, unnecessarily consumes available system resources, and may result in a degradation to the service provided to the other mobile stations being served by a given base station.
Thus, there remains a need for alternative scheduling and/or packet filling techniques, advantageously techniques that are better adapted to the downlink transmissions of VoIP data on high speed packet data channels.